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\f0\b\fs24 \cf0 American Cities Most Threatened by Rising Sea Levels
\b0 \
by Andrew Freedman\
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\cf0 Oct. 12, 2015 \'96 Steep cuts in greenhouse gas (GHG) emissions could lessen the threat that sea level rise poses to iconic American cities during the coming centuries, by more than half, according to a new study published Monday.\
By contrast, if emissions were to follow a so-called "business as usual" trajectory, between 14 to 33 feet of global average sea level rise would be locked into the climate system. That would submerge land that is currently home to between 20 and 31 million Americans. It includes more than 20 cities with populations of 100,000 or more, as well as the majority of residents in many smaller cities, the study found.\
The study, published Monday in the journal
\i Proceedings of the National Academy of Sciences
\i0 , is the first to examine how the energy choices made in the next few decades \'97 including at a pivotal climate summit in Paris that begins at the end of November \'97 will affect coastal U.S. cities, down to the zip code level for generations to come.\
The study provides an estimate of the population on land that can avoid the threat of future submergence, if we follow a low-emissions pathway instead of the current trajectory of business-as-usual emissions.\
In New York City, for example, the contrast between the high emissions scenario and low emissions scenario would mean be the difference between submerging all of newly trendy Red Hook and Cobble Hill neighborhoods in Brooklyn, New York, as well as the new Brooklyn Bridge Park and a swath of prized real estate in southwest Manhattan, versus keeping those areas dry.\
New York City ranks at the top of the list of population size that can avoid submergence. There, att least 1.6 million people could avoid a watery future, if major emissions cuts are achieved in the near future.\
The cities of Jacksonville, Virginia Beach, Sacramento and Miami follow New York, in terms of the size of the population that could avoid submergence, if steep carbon cuts were to take place in the next couple of decades, versus a business-as-usual course, according to data provided by the study's authors.\
In Virginia Beach, for example, the difference between a high and low emissions scenario means the contrast between seeing the entire city submerged under the Atlantic, and only a portion of it reclaimed by the sea.\
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\i \cf0 Long-Term "Cultural Legacy" at Risk\
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\i0 \cf0 The study raises the possibility that the cultural legacy of cities, ranging from New York to Boston to Miami and New Orleans, are at existential risk.\
The work is by a team from
\i Climate Central
\i0 , a New Jersey-based research and journalism organization, and the Potsdam Institute for Climate Impact Research in Germany. It is accompanied by a website, where one can search by zip code, to see how individual towns will fare under various emissions scenarios and ice sheet melt scenarios.\
"If we don't cut carbon emissions very sharply and quickly, we could effectively be sacrificing a whole U.S. state," said Ben Strauss, the lead author of the study, in an email to
\i Mashable
\i0 . "We could lock in enough sea level rise to lose land home to more Americans than live in any state except California."\
The study is unique in that\
\'95 it examines the point by which a particular amount of sea level rise would be locked into, or committed, by the climate system;\
\'95 it examines the point by which a particular amount of sea level rise would be locked into, or committed, by the climate system.\
This occurs because CO
\fs20 2
\fs24 , the main GHG, can remain in the air for centuries, and the oceans and giant ice sheets of Greenland and Antarctica respond to warming temperatures over centuries to millennia.\
For example, the study says that the world is already likely to see 1.6 meters, or about 5.2 feet, of global sea level rise compared to the present level, because of the cumulative GHG emissions through this year alone.\
Sea-level rise commitment reaches a median estimate of 7.9 feet, or 2.4 meters, to 23 feet, or 7.1 meters, by the end of the century under a low or high emissions scenario. (Local amounts of sea level rise would be higher or lower than that, depending on ocean currents, the rate of sinking land, etc.)\
The amount of sea level rise that is already in the climate change pipeline, simply because of the amount of GHGs already emitted, means that about 414 U.S. municipalities will see more than 50% of their populated area fall below the future high tide line, thereby affecting at least 6.2 million people, the study found.\
Aggressive carbon cuts, which would have to be larger than the cuts currently being discussed in the run-up to the Paris Climate Summit, could cut the number of communities threatened by long-term sea level rise by more than half, the study found.\
"We lock in starkly different futures, depending upon the choices we make," Strauss wrote. "Without extremely steep and rapid carbon cuts, sea level rise will become an existential threat for more than 1,000 American towns and cities.\'94\
For example, for Florida, which is the most threatened state by sea level rise, aggressive global carbon emissions cuts could prevent the submergence of land that is now home to about 5.6 million people, as compared to unabated emissions.\
Jacksonville, Miami, and Fort Lauderdale have some of the largest implicated populations in the state, with 411,000, 399,000, and 165,000 people respectively, if current global emissions levels continue through the year 2100. With aggressive emissions cuts, however these numbers would fall to about 63,000, 208,000 and 147,000, respectively.\
After Florida, the next 3 most affected states are California, Louisiana and New York, in different orders for different scenarios.\
"This work looks reasonable and useful," said Richard Alley. He is a geosciences professor at Penn State University who specializes in studying the world's ice sheets, which are the key driver of future sea level rise. Alley was not involved in the new study. "The fossil fuels we are burning accumulated over a few hundred million years, and we are burning them over a few hundred years, roughly a million times faster than nature saved them for us, and much faster than nature can make new ones," Alley wrote in an email to
\i Mashable
\i0 .\
"A transition to a different energy source is not optional, although we can choose to delay a little or not. The evidence from many studies is strong that, if the start of serious effort to make the transition is delayed a few decades or more, we will commit to large climate and sea-level changes that may persist further into the future than the history of civilization extends into the past," Alley wrote.\
For some places, like New Orleans, there has already been enough GHGs emitted into the atmosphere to ensure a long-term sea level rise that would submerge the entire population of the city, provided no effective adaptation efforts are taken to keep the water out, the study found.\
"Although past [manmade] emissions already have caused sea-level commitment that will force coastal cities to adapt, future emissions will determine which areas we can continue to occupy or may have to abandon," the study states.\
This means that the amount of sea level rise set into motion, by the rise in GHGs and global temperatures through 2015, won't be fully realized until well beyond the year 2100, but that such an increase could be large enough to swamp the cultural legacy of historic sites in cities such as Boston, New York and Annapolis, Maryland.\
In other words, the study may not be relevant to making a decision on whether or not you should buy an oceanfront home \'97 although there is plenty of other evidence suggesting that the answer to this question would be "no.\'94 But it provides insight to urban policy makers and national political leaders, who are putting coastal infrastructure and emissions plans in place that could dramatically alter the future course of and resilience to sea level rise.\
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\cf0 mashable.com/2015/10/12/sea-level-rise-submerge-us-cities/#1g0xgxvVQuqL}